The transporting of petroleum products on tank ships requires gauging the tanks on loading and before discharge to determine the quantities of product transported. The large quantities involved with their high costs eliminate the use of automatic gauging systems due to their large errors. The transfer of cargo is based on physical ullages measured with a tape by an independent gauger.
Portable ullage measuring devices providing a method of finding the surface of a liquid in a tank without visual sighting are well known and reference is made to my U.S. Pat. No. 4,123,753-W, H. Gravert, disclosing an accurate form of such device.
Ecology and vessel safety have added inert gas with closed loading and discharge practices to the transportation of cargoes. The new inert gas system pressurize the cargo tanks, making it impossible to guage a tank through the ullage port without first lowering the inert gas pressure. The excess inert gas and petroleum vapors are vented to atmosphere, then the tank is gauged by a hand tape using the edge of the ullage port as the standard reference. It is from this edge that the tank volume is calibrated.
It is also known to gauge and sample contents of pressurized tanks and reference is made to U.S. Pat. No. 2,284,396 W. Pfeiffer.
Systems such as disclosed in the Pfeiffer Patent require expensive duplication at each ullage port, or the transporting of a portion of heavy cumbersome equipment between ullage ports.
In my co-pending application there is disclosed and claimed a lightweight hand gauge mechanism in association with a tank outlet port sized to receive the gauging equipment.